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ENCYCLOPEDIA- Volume 2

1.
G
Gamma Ray
Gamma radiation, also known as gamma rays, and denoted by the
Greek letter γ, refers to electromagnetic radiation of extremely
high frequency and therefore high energy per photon. Gamma rays
are ionizing radiation, and are thus biologically hazardous.
They are classically produced by
the decay from high energy states
of atomic nuclei (gamma decay),
but are also created by other
processes. Paul Villard, a French
chemist and physicist, discovered
gamma radiation in 1900, while
studying radiation emitted from
radium. Villard's radiation was
named "gamma rays" by Ernest
Rutherford in 1903.
Natural sources of gamma rays on
Earth include gamma decay from
naturally occurring
radioisotopes, and secondary
radiation from atmospheric
interactions with cosmic ray
particles. Rare terrestrial
natural sources produce gamma
rays that are not of a nuclear
origin, such as lightning strikes and terrestrial gamma-ray
flashes. The electron avalanche builds up quickly, generating
more and more high energy particles, in an ever increasing
feedback loop, eventually generating a terrestrial gamma ray
flash. Gamma rays are produced by a number of astronomical
processes in which very high-energy electrons are produced, that
in turn cause secondary gamma rays by the mechanisms of
Gamma Ray Radiation

2.
bremsstrahlung, inverse Compton scattering and synchrotron
radiation. A large fraction of such
41
astronomical gamma rays are screened by Earth's atmosphere and
can only be detected by spacecraft.
Gamma rays typically have frequencies above 10 exahertz (or >1019
Hz), and therefore have energies above 100 keV and wavelengths
less than 10 picometers (less than the diameter of an atom).
However, this is not a hard and fast definition, but rather only
a rule-of-thumb description for natural processes. Gamma rays
from radioactive decay are defined as gamma rays no matter what
their energy, so that there is no lower limit to gamma energy
derived from radioactive decay. Gamma decay commonly produces
energies of a few hundred keV, and almost always less than 10
MeV. In astronomy, gamma rays are defined by their energy, and
no production process need be specified. The energies of gamma
rays from astronomical sources range over 10 TeV, at a level far
too large to result from radioactive decay. [2]
A notable example
is extremely powerful bursts of high-energy radiation normally
referred to as long duration gamma-ray bursts, which produce
gamma rays by a mechanism not compatible with radioactive decay.
These bursts of gamma rays, thought to be due to the collapse of
stars called hypernovae, are the
most powerful events so far
discovered in the cosmos.
Geiger, Hans Wilhelm
( 1882-1945)
September 30, 1882, Neustadt an de
Haardt, Germany, d. September 24, 1945,
Potsdam. A German physicist and
inventor of the Geiger counter, a type
of particle detector, and for the
Geiger-Marsden experiment which
discovered the atomic nucleus. In 1902
, Geiger started studying physics and
mathematics in the University of Erlangen and was awarded a doctorate
in 1986. In 1907 he began work with Ernest Rutherford at the
Hans Wilhelm "Gengar" Geiger (1928)

3.
University of Manchester, the following year he built his first device
to detect radioactive
42
particles and became known as Geiger Counter. The detection component
ofGeiger Counter as a metal tube filled with gas under low pressure.
The tube and a copper cathodes are under high voltage. When alpha
particle emitted from the nucleus of a radioactive atom passes through
the tube, it ionizes a gas molecule leaving the molecule or ion, is
then attracted to the cathode. As it moves toward the cathode, the ion
collides with other gas molecule s and produces more ions. This brief
cascade of ions creates sufficient energy to produce a momentarily
electrical current. The Geiger Counter records each cascade
electronically and indicates a cascade with a click. Rapidly repeating
clicks indicates the presence or a huge number of alpha particles and
therefore an increased level of radioactivity. Rutherford subsequently
identified the alpha particles as the nucleus of helium atom.
In 1909, along with Ernest Marsden, conducted the famous Geiger-
Marsden experiment, also called the ― gold-foil experiment‖. And also
along with Ernest Rutherford, they created the Rutherford-Geiger tube,
later to become Geiger counter. In 1911, Geiger and John Mitchel
Nuttall discovered the Geiger-Nuttall law and performed experiments
that led to Rutherford’s atomic model.
In 1928, Geiger and his student, Walter Muller created an improved
version of Geiger counter, called as the Geiger-Muller counter. Geiger
also worked with James Chadwick. In 1912, leader became the leader of
the Physical-Technical Reichsanstalt in
Berlin. In 1925, became professor in Kiel,
in 1929 in Tubingen and from 1936 in
Berlin. He was a member of Uranium Club. He
expressed himself in public about the
Nazis. But illness slowed the pace of
Geiger’s work from 1940 until his death.
Giauque, William Francis
(1895-1982)
b. May 12, 1895 On t. , Canada, d. March
28, 1982, Berkeley, California, U.S.A.
Geiger, Hans Wilhelm

4.
A Canadian- born American physical chemist and winner at the Nobel
Prize for chemistry in 1949 for his studies of the properties of
matter at temperatures close
43
to absolute zero. After earning his Ph. D. from the University of
California, Berkeley in 1922, Giauque joined the chemistry faculty
there and held posts at the school until 1981. In 1927, he proposed a
new method of achieving extremely low temperatures using a process
called adiabatic demagnetization. By 1933, he had working apparatus
that obtained a temperature with one-tenth of a degree of absolute
zero ( -273.15 degree Celsius). His researched confirmed the third law
of thermodynamics, which states that the entropy of ordered solids
reaches zero at the absolute zero of temperature. In the course of his
low-temperature studies of oxygen, Giauque discovered with Herrick L.
Johnston the oxygen isotopes of mass 17 and 18. For his work in
chemical thermodynamics, he
received the 1949 Nobel Prize
in Chemistry.
Gummite
It is a mixture of natural
Uranium oxides,
representing the final
oxidation and hydration stages of uraninite, that usually occurs
as dense masses and crusts in many of the known uraninite
localities. It is named for its gum-like consistence. The
material was also known under various names, mostly because of
different origins of the samples, including: eliasite from Elias
– the name of a mine at Jáchymov, coracite – a variety from Lake
Superior, pittinite, pechuran, urangummit and uranogummite.
It varies widely in physical appearance of some varieties, is related
to well-defined Uranium oxides such as limonite and also manganese
oxides.
Gummite from collection of Prague
National Museum

5.
44
Gyroscope
A gyroscope is a device for
measuring or maintaining
orientation, based on the
principles of angular momentum.
Mechanically, a gyroscope is a
spinning wheel or disc in which
the axle is free to assume any
orientation. Although this
orientation does not remain fixed,
it changes in response to an
external torque much less and in a
different direction than it would
with the large angular momentum associated with the disc's high
rate of spin and moment of inertia. The device's orientation
remains nearly fixed, regardless of the mounting platform's
motion, because mounting the device in a gimbal minimizes
external torque.
Gyroscopes based on other operating principles also exist, such
as the electronic, microchip-packaged MEMS gyroscope devices
found in consumer electronic devices, solid-state ring lasers,
fibre optic gyroscopes, and the extremely sensitive quantum
gyroscope.
Applications of gyroscopes include inertial navigation systems
where magnetic compasses would not work (as in the Hubble
telescope) or would not be precise enough (as in ICBMs), or for
the stabilization of flying vehicles like radio-controlled
helicopters or unmanned aerial vehicles. Due to their precision,
gyroscopes are also used in gyrotheodolites to maintain
direction in tunnel mining.

6.
45
H
Heart
The heart is a hollow muscular organ that pumps blood throughout
the blood vessels to various parts of the body by repeated,
rhythmic contractions. It is found in all animals with
a circulatory system, which includes the vertebrates.
The adjective cardiac means "related to the heart" and comes
from the Greek καρδιά, kardia, for "heart". Cardiology is the
medical speciality that deals with cardiac diseases and
abnormalities. The vertebrate heart is principally composed
of cardiac muscle and connective tissue. Cardiac muscle is an
involuntary striated muscle tissue specific to the heart and is
responsible for the heart's ability to pump blood.
The average human heart, beating at 72 beats per minute, will
beat approximately 2.5 billion times during an average 66 year
lifespan, and pumps approximately 4.7-5.7 litres of blood per
minute. It weighs approximately 250 to 300 grams (9 to 11 oz) in
females and 300 to 350 grams (11 to 12 oz) in males. The
structure of the heart can vary among the
different animal species.Cephalopods have two "gill hearts" and
one "systemic heart". In vertebrates, the heart lies in the
anterior part of the body cavity, dorsal to the gut. It is
always surrounded by a pericardium, which is usually a distinct
structure, but may be continuous with the peritoneum in jawless
and cartilaginous fish. Hagfish, uniquely among vertebrates,
also possess a second heart-like structure in the tail.
Structure diagram of the human heart from an anterior view. Blue
components indicate deoxygenated blood pathways and red
components indicate oxygenated pathways.

7.
The adult human heart has a mass of between 250 and 350 grams
46
and is about the size of a fist. It is located anterior to the
vertebral column and posterior to the sternum.
It is enclosed in a double-walled sac called the pericardium.
The pericardium's outer wall is called the parietal pericardium
and the inner one the visceral pericardium. Between them there
is some pericardial fluid which functions to permit the inner
and outer walls to slide easily over one another with the heart
movements. Outside the parietal pericardium is a fibrous layer
called thefibrous pericardium which is attached to the
mediastinal fascia. This
sac protects the heart
and anchors it to the
surrounding structures.
The outer wall of the
human heart is composed
of three layers; the
outer layer is called
the epicardium, or
visceral pericardium
since it is also the
inner wall of the
pericardium. The middle
layer is called
the myocardium and is composed of contractile cardiac muscle. In
mammals, the function of the right side of the heart is to
collect de-oxygenated blood, in the right atrium, from the body
(via superior and inferior vena cavae) and pump it, through the
tricuspid valve, via the right ventricle, into the lungs
(pulmonary circulation) so that carbon dioxide can
be exchanged for oxygen. This happens through the passive
process of diffusion. The left side (see left heart) collects
oxygenated blood from thelungs into the left atrium. From the
left atrium the blood moves to the left ventricle, through the
bicuspid valve (mitral valve), which pumps it out to the body
(via the aorta). On both sides, the lower ventricles are thicker
and stronger than the upper atria. The muscle wall surrounding
the left ventricle is thicker than the wall surrounding the
right ventricle due to the higher force needed to pump the blood
through the systemic circulation.

8.
47
Heat Energy
Heat energy is a form of
energy that results from movement
of atoms, ions or molecules in
solids liquids or gases. It can
be transferred from one object to
another if the two objects have a
temperature difference.
Thermal energy is generated and
measured by heat of any kind. It
is caused by the increased
activity or velocity of molecules in a substance, which in turn
causes temperature to rise accordingly.
There are many natural sources of thermal energy on Earth,
making it an important component of alternative energy.
Heat energy is the type of energy that is emitted from burning
fuel. A unit of heat energy is defined as the amount of heat
required to raise the temperature of one pound of water by one
degree Fahrenheit.
Heat energy deals with the transfer of energy of a body or of a
system in the form of heat, or raising temperatures. Raising the
temperature of a substance, raises it's heat energy.
The movement of atoms and molecules create heat energy. It
transfers among particles in a give substance by kinetic energy
which means that the heat is transferred by bouncing particles
bumping into each other.
Hemoglobin
Hemoglobin (/hiːməːɡloʊbɪn/); also spelled haemoglobin and
abbreviated Hb or Hgb, is the iron-containing oxygen-
transport metalloproteinase in the red blood cells of
all vertebrates[1]
(with the exception of the fish family

9.
48
Channichthyidae) as well as the tissues of some invertebrates.
Hemoglobin in the blood carries oxygen from the respiratory
organs (lungs or gills) to the rest of the body (i.e. the
tissues) where it releases the oxygen to burn nutrients to
provide energy to power the functions of the organism in the
process called metabolism.
In mammals, the protein makes up about 96% of the red blood
cells' dry content (by weight), and around 35% of the total
content (including water. Hemoglobin has an oxygen binding
capacity of 1.34 mL O2 per gram of hemoglobin, which increases
the total blood oxygen capacity seventy-fold compared to
dissolved oxygen in blood. The mammalian hemoglobin molecule can
bind (carry) up to four oxygen molecules.
Hemoglobin is involved in the transport of other gases: it
carries some of the body's respiratory carbon dioxide (about 10%
of the total) ascarbaminohemoglobin, in which CO2 is bound to the
globin protein. The molecule also carries the important
regulatory molecule nitric oxide bound to a globin
protein thiol group, releasing it at the same time as oxygen.
Hemoglobin and hemoglobin-like molecules are also found in many
invertebrates Hemoglobin is also found outside red blood cells
and their progenitor lines. Other cells that contain hemoglobin
include the A9 dopaminergic neurons in the substantial
nigra, macrophages, alveolar cells, and meningeal cells in the
kidney. In these tissues, hemoglobin has a non-oxygen-carrying
function as an antioxidant and a regulator of iron metabolism.
In these organisms, hemoglobin’s may carry oxygen, or they may
act to transport and regulate other things such as carbon
dioxide, nitric oxide, hydrogen sulfide and sulfide. A variant
of the molecule, called leg hemoglobin, is used to scavenge
oxygen away from anaerobic systems, such as the nitrogen-fixing
nodules of leguminous plants, before the oxygen can poison the
system. Hemoglobin consists mostly of protein subunits (the
"globin" molecules), and these proteins, in turn, are folded
chains of a large number of different amino acids
called polypeptides. The amino acid sequence of any polypeptide
created by a cell is in turn determined by the stretches of DNA
called genes. In all proteins, it is the amino acid sequence
which determines the protein's chemical properties and function.
There is more than one hemoglobin gene. The amino acid sequences
of the globin proteins in hemoglobins usually differ between
species. These differences grow with evolutionary distance

10.
49
between species. For example, the most common hemoglobin
sequences in humans and chimpanzees are nearly identical,
differing by only one amino acid in both the alpha and the beta
globin protein chains. These differences grow larger between
less closely related species.
Even within a species, different variants of hemoglobin always
exist, although one sequence is usually a "most common" one in
each species. Mutations in the genes for the
hemoglobin protein in a species result in hemoglobin
variants. Many of these mutant forms of hemoglobin cause no
disease. Some of these mutant forms of hemoglobin, however,
cause a group of hereditary diseases termed
the hemoglobinopathies. The best known hemoglobinopathy
is sickle-cell disease,
which was the first human
disease
whose mechanism was
understood at the
molecular level. A
(mostly) separate set of
diseases
called thalassemias invol
ves underproduction of
normal and sometimes
abnormal hemoglobins, through problems and mutations in
globin gene regulation. All these diseases produce anemia.
Variations in hemoglobin amino acid sequences, as with other
proteins, may be adaptive. For example, recent studies have
suggested genetic variants in deer mice that help explain how
deer mice that live in the mountains are able to survive in the
thin air that accompanies high altitudes.
Hydroelectricity
Use running water to generate electricity, whether it's a small
stream or a larger river.
Small or micro hydroelectricity systems, also called hydropower
systems or just hydro systems, can produce enough electricity

11.
50
for lighting and electrical appliances in an average home.
How do hydropower systems work?
All streams and rivers flow downhill. Before the water flows
down the hill, it has potential energy because of its height.
Hydro power systems convert this potential energy into kinetic
energy in a turbine, which drives a
generator to produce electricity.
The greater the height and the more
water there is flowing through the
turbine, the more electricity can
be generated.
The amount of electricity a system
actually generates also depends on
how efficiently it converts the
power of the moving water into
electrical power.
Hydrogen Bond
Polar molecules, such as water
molecules, have a weak, partial
negative charge at one region of the
molecule (the oxygen atom in water) and
a partial positive charge elsewhere
(the hydrogen atoms in water).
Thus when water molecules are close
together, their positive and negative
regions are attracted to the
oppositely-charged regions of nearby molecules. The force of
attraction, shown here as a dotted line, is called

12.
51
a hydrogen bond. Each water molecule is hydrogen bonded to four
others.
The hydrogen bonds that form between water molecules account for
some of the essential — and unique — properties of water.
The attraction created by hydrogen bonds keeps water liquid
over a wider range of temperature than is found for any
other molecule its size.
The energy required to break multiple hydrogen bonds causes
water to have a high heat of vaporization; that is, a large
amount of energy is needed to convert liquid water, where
the molecules are attracted through their hydrogen bonds,
to water vapor, where they are not.
Two outcomes of this:
The evaporation of sweat, used by many mammals to cool
themselves, cools by the large amount of heat needed to
break the hydrogen bonds between water molecules.
Reduction of temperature extremes near large bodies of
water like the ocean.
The hydrogen bond has only 5% or so of the strength of
a covalent bond. However, when many hydrogen bonds can form
between two molecules (or parts of the same molecule), the
resulting union can be sufficiently strong as to be quite
stable.
Multiple hydrogen bonds
hold the two strands of the DNA double helix together
hold polypeptides together in such secondary structures as
the alpha helix and the beta conformation;
help enzymes bind to their substrate
help antibodies bind to their antigen
help transcription factors bind to each other;
help transcription factors bind to DNA

13.
52
I
Ionic Bonding
Ionic bonding is a type of
chemical bonding that involves the
electrostatic attraction between
oppositely charged ions. These ions
represent atoms that have lost one
or more electron (known as cations)
and atoms that have gained one or
more electrons (known as an anions).
In the simplest case, the cation is
a metal atom and the anion is a nonmetal atom, but these ions
can be of a more complex nature, e.g. molecular ions like NH4
+
or
SO4
2-
It is important to recognize that clean ionic bonding - in which
one atom "steals" an electron from another - cannot exist: All
ionic compounds have some degree of covalent bonding, or
electron sharing. Thus, the term "ionic bonding" is given when
the ionic character is greater than the covalent character -
that is, a bond in which a large electronegativity difference
exists between the two atoms, causing the bonding to be more
polar (ionic) than in covalent bonding where electrons are
shared more equally. Bonds with partially ionic and partially
covalent character are called polar covalent bonds.
Ionic compounds conduct electricity when molten or in solution,
but typically not as a solid. There are exceptions to this rule,
such as rubidium silver iodide, where the silver ion can be
quite mobile. Ionic compounds generally have a high melting
point, depending on the charge of the ions they consist of. The

14.
higher the charges the stronger the cohesive forces and the
higher the melting point. They also tend to be soluble in water.
53
Here, the opposite trend roughly holds: The weaker the cohesive
forces the greater the solubility.
Formation
Ionic bonding can result from a redox reaction when atoms of an
element (usually metal), whose ionization energy is low, release
some of their electrons to achieve a stable electron
configuration. In doing so, cations are formed. The atom of
another element (usually nonmetal), whose electron affinity is
positive, then accepts the electron(s), again to attain a stable
electron configuration, and after accepting electron(s) the atom
becomes an anion. Typically, the stable electron configuration
is one of the noble gases for elements in the s-block and the p-
block, and particular stable electron configurations for d-block
and f-block elements. The electrostatic attraction between the
anions and cations leads to the formation of a solid with a
crystallographic lattice in which the ions are stacked in an
alternating fashion. In such a lattice, it is usually not
possible to distinguish discrete molecular units, so that the
compounds formed are not molecular in nature. However, the ions
themselves can be complex and form molecular ions like the
acetate anion or the ammonium
cation.
Insulin
Insulin is a peptide hormone,
produced by beta cells of the
pancreas, and is central to
regulating carbohydrate and
fat metabolism in the body.
It causes cells in the liver,
skeletal muscles, and fat tissue to absorb glucose from the
blood.
Insulin stops the use of fat as an energy source by inhibiting
the release of glucagon. With the exception of the metabolic
disorder diabetes mellitus and metabolic syndrome, insulin is
provided within the body in a constant proportion to remove

15.
excess glucose from the blood, which otherwise would be toxic.
When blood glucose levels fall below a certain level, the
54
body begins to use stored sugar as an energy source through
glycogenolysis, which breaks down the glycogen stored in the
liver and muscles into glucose, which can then be utilized as an
energy source. As a central metabolic control mechanism, its
status is also used as a control signal to other body systems
(such as amino acid uptake by body cells). In addition, it has
several other anabolic effects throughout the body.
When control of insulin levels fails, diabetes mellitus can
result. As a consequence, insulin is used medically to treat
some forms of diabetes mellitus. Patients with type 1 diabetes
depend on external insulin (most commonly injected
subcutaneously) for their survival because the hormone is no
longer produced internally.[2]
Patients with type 2 diabetes are
often insulin resistant and, because of such resistance, may
suffer from a "relative" insulin deficiency. Some patients with
type 2 diabetes may eventually require insulin if other
medications fail to control blood glucose levels adequately.
Over 40% of those with Type 2 diabetes require insulin as part
of their diabetes management plan.
The human insulin protein is composed of 51 amino acids, and has
a molecular weight of 5808 Da. It is a dimer of an A-chain and a
B-chain, which are linked together by disulfide bonds.
Insulin's name is derived from the Latin insula for "island".
Insulin's structure varies slightly between species of animals.
Insulin from animal sources differs somewhat in "strength" (in
carbohydrate metabolism control effects) from that in humans
because of those variations. Porcine insulin is especially close
to the human version.
Synthesis
Insulin is proIn mammals, insulin is synthesized in the pancreas
within the β-cells of the islets of Langerhans. One million to
three million islets of Langerhans (pancreatic islets) form the
endocrine part of the pancreas, which is primarily an exocrine
gland. The endocrine portion accounts for only 2% of the total
mass of the pancreas. Within the islets of Langerhans, beta
cells constitute 65–80% of all the cells.

16.
Insulin consists of two polypeptide chains, the A- and B-
chains, linked together by disulfide bonds. It is however first
synthesized as a single polypeptide called preproinsulin in
55
pancreatic β-cells. Preproinsulin contains a 24-residue signal
peptide which directs the nascent polypeptide chain to the rough
endoplasmic reticulum (RER). The signal peptide is cleaved as
the polypeptide is translocated into lumen of the RER, forming
proinsulin.[13]
In the RER the proinsulin folds into the correct
conformation and 3 disulfide bonds are formed. About 5–10 min
after its assembly in the endoplasmic reticulum, proinsulin is
transported to the trans-Golgi network (TGN) where immature
granules are formed. Transport to the TGN may take about 30 min.
In the posttranslational modifications insulin and its related
proteins have been shown to be produced inside the brain, and
reduced levels of these proteins are linked to Alzheimer's
disease.
duced in the pancreas and released when any of several stimuli
are detected. These stimuli include ingested protein and glucose
in the blood produced from digested food. Carbohydrates can be
polymers of simple sugars or the simple sugars themselves. If
the carbohydrates include glucose, then that glucose will be
absorbed into the bloodstream and blood glucose level will begin
to rise. In target cells, insulin initiates a signal
transduction, which has the effect of increasing glucose uptake
and storage. Finally, insulin is degraded, terminating the
response.
Iron
Iron is a chemical element with the
symbol Fe (from Latin: ferrum) and
atomic number 26. It is a metal in
the first transition series. It by
mass is the most common element on
Earth, forming much of Earth's outer
and inner core. It is the fourth most
1lustrous metallic with a grayish
tinge

17.
common element in the Earth's crust. Iron's very common presence
in rocky planets like Earth is due to its abundant production as
a result of fusion in high-mass stars, wherein the production of
nickel-56 (which decays to the most common isotope of iron) is
56
the last nuclear fusion reaction that is exothermic. Therefore,
radioactive nickel is the last element to be produced, before
collapse of a supernova causes the explosion that abundantly
scatters this precursor radionuclide into space.
Like other group 8 elements, iron exists in a wide range of
oxidation states, −2 to +6, although +2 and +3 are the most
common. Elemental iron occurs in meteoroids and other low oxygen
environments, but is reactive to oxygen and water. Fresh iron
surfaces appear lustrous silvery-gray, but oxidize in normal air
to give hydrated iron oxides, commonly known as rust. Unlike
many other metals which form passivating oxide layers, iron
oxides occupy more volume than iron metal, and thus iron oxides
flake off and expose fresh surfaces for corrosion.
Iron metal has been used since ancient times, though copper
alloys, which have lower melting temperatures, were used first
in history. Pure iron is soft (softer than aluminium), but is
unobtainable by smelting. The material is significantly hardened
and strengthened by impurities, such as carbon, from the
smelting process. A certain proportion of carbon (between 0.002%
and 2.1%) produces steel, which may be up to 1000 times harder
than pure iron. Crude iron metal is produced in blast furnaces,
where ore is reduced by coke to pig iron, which has a high
carbon content. Further refinement with oxygen reduces the
carbon content to the correct proportion to make steel. Steels
and low carbon iron alloys along with other metals (alloy
steels) are by far the most common metals in industrial use, due
to their great range of desirable properties and the abundance
of iron.
Iron chemical compounds, which include ferrous and ferric
compounds, have many uses. Iron oxide mixed with aluminium
powder can be ignited to create a thermite reaction, used in
welding and purifying ores. It forms binary compounds with the
halogens and the chalcogens. Among its organometallic compounds
is ferrocene, the first sandwich compound discovered.
Iron plays an important role in biology, forming complexes with
molecular oxygen in hemoglobin and myoglobin; these two

18.
compounds are common oxygen transport proteins in vertebrates.
Iron is also the metal used at the active site of many important
redox enzymes dealing with cellular respiration and oxidation
and reduction in plants and animals.
57
Isomer
In chemistry, isomers (/ːaɪsəmərz/; from Greek ἰ ζομερής,
isomerès; isos = "equal", méros = "part") are molecules with the
same molecular formula but different chemical structures. That
is, isomers contain the same number of atoms of each element,
but have different arrangements of their atoms in space.[1][2]
Isomers do not necessarily share similar properties, unless they
also have the same functional groups. There are many different
classes of isomers, like positional isomers, cis-trans isomers
and enantiomers, etc. (see chart below). There are two main
forms of isomerism: structural isomerism and stereoisomerism
(spatial isomerism)
Structural isomers
In structural isomers, sometimes referred to as constitutional
isomers, the atoms and functional groups are joined together in
different ways. Structural isomers have different IUPAC names
and may or may not belong to the same functional group.[3]
This
group includes chain isomerism whereby hydrocarbon chains have
variable amounts of branching; position isomerism, which deals
with the position of a functional group on a chain; and

19.
functional group isomerism, in which one functional group is
split up into different ones.
For example, two position isomers would be 2-fluoropropane and
1-fluoropropane, illustrated on the left side of the diagram
above.
58
In skeletal isomers the main carbon chain is different between
the two isomers. This type of isomerism is most identifiable in
secondary and tertiary alcohol isomers.
Tautomers are structural isomers of the same chemical substance
that spontaneously interconvert with each other, even when pure.
They have different chemical properties and, as a consequence,
distinct reactions characteristic to each form are observed. If
the interconversion reaction is fast enough, tautomers cannot be
isolated from each other. An example is when they differ by the
position of a proton, such as in keto/enol tautomerism, where
the proton is alternately on the carbon or oxygen.
Stereoisomer In stereoisomers the bond structure is the same,
but the geometrical positioning of atoms and functional groups
in space differs. This class includes enantiomers, which are
non-superimposable mirror-images of each other, and
diastereomers, which are not. Enantiomers always contain chiral
centres and diastereomers often do, but there are some
diastereomers that neither are chiral nor contain chiral
centers.[4]
Another type of isomer, conformational isomers
(conformers), may be rotamers, diastereomers, or enantiomers
depending on the exact compound. For example, ortho- position-
locked biphenyl systems have enantiomers.
E/Z isomers, which have restricted rotation within the molecule,
to be specific isomers containing a double bond, are
configurational isomers. They are classified as diastereomers,
whether or not they contain any chiral centres.[4]
E/Z notation
depicts absolute stereochemistry, which is an unambiguous
descriptor based on CIP priorities.
"Cis–trans isomers" are used to describe any molecules with
restricted rotation in the molecule. However, these descriptors
describe relative stereochemistry only based on group bulkiness
or principal carbon chain, so can be ambiguous. This is
especially problematic for double bonds that have more than two
substituents. An obsolete term for cis–trans isomerism is

20.
"geometric isomerism".[5]
For alkenes with more than two
substituents, E-Z notation is used instead of cis and trans. If
possible, E and Z (written in italic type) is also preferred in
compounds with two substituents.[6]
In octahedral coordination compounds, facial–meridional
isomerism occurs. The isomers can be fac- (with facial ligands)
59
or mer- (with meridional ligands).
Note that, although conformers can be referred to as
stereoisomers, they are not stable isomers, since bonds in
conformers can easily rotate, thus converting one conformer to
another, which can be either diastereomeric or enantiomeric to
the original one.
While structural isomers typically have different chemical
properties, stereoisomers behave identically in most chemical
reactions, except in their reaction with other stereoisomers.
Enzymes, however, can distinguish between different enantiomers
of a compound, and organisms often prefer one isomer over the
other. Some stereoisomers also differ in the way they rotate
polarized light.
Isomerization
Isomerization is the process by which one molecule is
transformed into another molecule that has exactly the same
atoms, but the atoms are rearranged.[7]
In some molecules and
under some conditions, isomerization occurs spontaneously. Many
isomers are equal or roughly equal in bond energy, and so exist
in roughly equal amounts, provided that they can interconvert
relatively freely, that is the energy barrier between the two
isomers is not too high. When the isomerization occurs
intramolecularly, it is considered a rearrangement reaction.
An example of an organometallic isomerization is the production
of decaphenylferrocene, [(η5
-C5Ph5)2Fe] from its linkage
isomer.[8][9]

21.
60
J
Jade
Jade is an ornamental rock. The term jade is applied to two
different metamorphic rocks that are made up of
different silicate minerals:
Nephrite consists of a microcrystalline interlocking fibrous
matrix of the calcium, magnesium-iron rich amphibole mineral
series tremolite (calcium-magnesium)-ferroactinolite (calcium-
magnesium-iron). The middle member of this series with an
intermediate composition is called actinolite (the silky
fibrous mineral form is one form of asbestos). The higher the
iron content the greener the colour.
Jadeite
Jadeite is a sodium- and aluminium-rich pyroxene. The gem
form of the mineral is a microcrystalline interlocking crystal

22.
matrix. A high pressure
clinopyroxene that is frequently
carved and polished as a
gemstone. Jadeite is
a pyroxene mineral with
composition NaAlSi2O6. It
is monoclinic. It has a Mohs
hardness of about 6.5 to 7.0
61
depending on the composition. The
mineral is dense, with a specific gravity of about 3.4. Jadeite
forms solid solutions with other pyroxene endmembers such
asaugite and diopside (CaMg-rich endmembers), aegirine (NaFe
endmember), and kosmochlor (NaCr endmember). Pyroxenes rich in
both the jadeite and augite endmembers are known as omphacite.
Jasper
A variety of colored chert,
typically red or green and often
found in association with iron
ores. Jasper is frequently used as
a gemstone or in the production of
ornaments.
The name means "spotted or speckled
stone", and is derived via Old
French jaspre (variant of Anglo-Norman jaspe) and Latin iaspidem
(nom. iaspis)) from Greek ἴ αζπις iaspis, (feminine noun)[5]
from
a Semitic language (cf. Hebrew ‫יושפה‬yushphah, Akkadian
yashupu).
Green jasper was used to make bow drills in Mehrgarh between 4th
and 5th millennium BC. Jasper is known to have been a favorite
gem in the ancient world; its name can be traced back in Arabic,
Persian, Hebrew, Assyrian, Greek and Latin. On Minoan Crete,

23.
jasper was carved to produce seals circa 1800 BC, as evidenced
by archaeological recoveries at the
palace of Knossos.
62
Jolly Balance
The Jolly balance is an instrument for
determining specific gravities. Invented
by the German physicist Philipp von
Jolly in 1864, it consists of
a spring fastened at the top to a
movable arm. At the lower end, the
spring is provided with two small pans,
one suspended beneath the other. The
lower pan is kept immersed to the same
depth in water, while the other one
hangs in the air. On the upright stand behind the spring is a
mirror on which is engraved or painted a scale of equal parts.
The specific gravity of an object, typically a solid, is
determined by noting how much the spring lengthens spring when
the object is resting in the upper pan in air ( ), and then when
the object is moved to the lower pan and immersed in water ( ).
The specific gravity is .
Juvenile water or
Magmatic water
A spring balance used in the
determination of specific
gravity.
Magmatic water or juvenile
water is water that exists
within, and in equilibrium with,
a magma or water
rich volatile fluids that are
derived from a magma. This

24.
magmatic water is released to the atmosphere during
a volcanic eruption. Magmatic water may also be released
as hydrothermal fluids during
63
the late stages of magmatic crystallization or solidification
within the Earth's crust. The crystallization
of hydroxyl bearing amphibole and mica minerals acts to contain
part of the magmatic water within a solidified igneous rock.
Ultimate sources of this magmatic water includes water and
hydrous minerals in rocks melted during subduction as well
as primordial water brought up from the deep mantle.
Juvenile Water:
Water that is new to the hydrologic cycle. Brought to Earth's
surface through volcanic eruptions.

25.
64
K
Kelp
Kelps are large seaweeds (algae) belonging to the brown
algae(Phaeophyceae) in the order Laminariales. There are about
30 differentgenera.
Kelp grows in underwater "forests" (kelp forests) in shallow
oceans, and is thought to have appeared in the Miocene, 23 to 5
million years ago. The organisms require nutrient-rich water
with temperatures between 6 and 14 °C (43 and 57 °F). They are
known for their high growth rate — the
generaMacrocystis and Nereocystis can grow as fast as half a
metre a day, ultimately reaching 30 to 80 metres (100 to
260 ft).

26.
Through the 19th century, the
word "kelp" was closely associated
with seaweeds that could be burned
to obtain soda ash (primarily
sodium carbonate). The seaweeds
used included species from both
the orders Laminariales
and Fucales. The word "kelp" was
also used directly to refer to
these processed ashes.
Ketone
A ketone (alkanone) /ːkiːtoʊn/ is an organic compound with the
structure RC(=O)R', where R and R' can be a variety of carbon-
containing substituents. Ketones feature a carbonyl group (C=O)
bonded to two other carbon atoms. Many ketones are known and
65
many are of great importance in industry and in biology.
Examples include many sugars (ketoses) and the industrial
solvent acetone.
Nomenclature and etymology
The word ketone derives its name from Aketon, an old German word
for acetone.
According to the rules of IUPAC nomenclature, ketones are named
by changing the suffix -ane of the parent alkane to -anone. For
the most important ketones, however, traditional nonsystematic
names are still generally used, for example acetone and
benzophenone. These nonsystematic names are considered retained
IUPAC names, although some introductory chemistry textbooks use
names such as 2-propanone or propan-2-one instead of acetone,
the simplest ketone (C H3-CO-CH3). The position of the carbonyl
group is usually denoted by a number.
Although used infrequently, oxo is the IUPAC nomenclature for a
ketone functional group. Other prefixes, however, are also used.
For some common chemicals (mainly in biochemistry), keto or oxo
refer to the ketone functional group. The term oxo is used
widely through chemistry. For example, it also refers to an
oxygen atom bonded to a transition metal (a metal oxo).

27.
Classes of ketones
Ketones are classified on the basis of their substituents. One
broad classification subdivides ketones into symmetrical and
asymmetrical derivatives, depending on the equivalency of the
two organic substituents attached to the carbonyl center.
Acetone and benzophenone (C6H5C(O)C6H5) are symmetrical ketones.
Acetophenone (C6H5C(O)CH3) is an asymmetrical ketone. In the
area of stereochemistry, asymmetrical ketones are known for
being prochiral.
Diketones
Many kinds of diketones are known, some with unusual properties.
66
The simplest is diacetyl (CH3C(O)C(O)CH3), once used as butter-
flavoring in popcorn. Acetylacetone (pentane-2,4-dione) is
virtually a misnomer (inappropriate name) because this species
exists mainly as the monoenol CH3C(O)CH=C(OH)CH3. Its enolate is
a common ligand in coordination chemistry.
Unsaturated ketones
Ketones containing alkene and alkyne units are often called
unsaturated ketones. The most widely used member of this class
of compounds is methyl vinyl ketone, CH3C(O)CH=CH2, which is
useful in the Robinson annulation reaction. Lest there be
confusion, a ketone itself is a site of unsaturation; that is,
it can be hydrogenated.
Cyclic ketones
Many ketones are cyclic. The simplest class have the formula
(CH2)nCO, where n varies from 3 for cyclopropanone to the teens.
Larger derivatives exist. Cyclohexanone, a symmetrical cyclic
ketone, is an important intermediate in the production of nylon.
Isophorone, derived from acetone, is an unsaturated,
asymmetrical ketone that is the precursor to other polymers.
Muscone, 3-methylpentadecanone, is an animal pheromone. Another
cyclic ketone is cyclobutanone, having the formula C4H6O.

28.
Kinetics
The cars of a roller coaster reach their maximum kinetic energy
when at the bottom of their path. When they start rising, the
kinetic energy begins to be converted to gravitational potential
energy. The sum of kinetic and potential energy in the system
remains constant, ignoring losses to friction.
Common symbol(s): KE, Ek, or T SI unit: joule (J)
Derivations from other quantities: Ek = ½mv2 Ek = Et+Er
The kinetic energy of an object is the energy which it
possesses due to its motion.[1] It is defined as the work needed
to
67
accelerate a body of a given mass from rest to its stated
velocity. Having gained this energy during its acceleration, the
body maintains this kinetic energy unless its speed changes. The
same amount of work is done by the body in decelerating from its
current speed to a state of rest.
In classical mechanics, the kinetic energy of a non-rotating
object of mass m traveling at a speed v is ½ mv². In
relativistic mechanics, this
is only a good approximation
when v is much less than the
speed of light.
K- Potassium
Potassium is a chemical
element with symbol K (from
Neo-Latin kalium) and atomic
number 19. Elemental
potassium is a soft silvery-
white alkali metal that
oxidizes rapidly in air and
is very reactive with water,
generating sufficient heat
to ignite the hydrogen
emitted in the reaction and burning with a lilac flame.

29.
Naturally occurring potassium is composed of three isotopes, one
of which, 40K, is radioactive. Traces (0.012%) of this isotope
are found in all potassium making it the most common radioactive
element in the human body and in many biological materials, as
well as in common building materials such as concrete.
Potassium ions are necessary for the function of all living
cells. Potassium ion diffusion is a key mechanism in nerve
transmission, and potassium depletion in animals, including
humans, results in various cardiac dysfunctions. Potassium
accumulates in plant cells, and thus fresh fruits and vegetables
are a good dietary source of it. This resulted in potassium
first being isolated from potash, the ashes of plants, giving
the element its name. For the same reason, heavy crop production
rapidly depletes soils of potassium, and agricultural
fertilizers consume 95% of global potassium chemical production.
68
Krypton
Krypton (from Greek: κρσπτός kryptos "the hidden one") is a
chemical element with symbol Kr and atomic number 36. It is a
member of group 18 (noble gases) elements. A colorless,
odorless, tasteless noble gas, krypton
occurs in trace amounts in the
atmosphere, is isolated by fractionally
distilling liquified air, and is often
used with other rare gases in
fluorescent lamps. Krypton is inert for
most practical purposes.
Krypton, like the other noble gases, can
be used in lighting and photography.
Krypton light has a large number of
spectral lines, and krypton's high light
output in plasmas allows it to play an
important role in many high-powered gas
lasers (krypton ion and excimer lasers), which pick out one of
the many spectral lines to amplify. There is also a specific
krypton fluoride laser. The high power and relative ease of
operation of krypton discharge tubes caused (from 1960 to 1983)
the official length of a meter to be defined in terms of the
wavelength of the 605 nm (orange) spectral line of krypton-86

30.
Krypton is characterized by several sharp emission lines
(spectral signatures) the strongest being green and yellow.[9]
It
is one of the products of uranium fission.[10]
Solidified krypton
is white and crystalline with a face-centered cubic crystal
structure, which is a common property of all noble gases (except
helium, with a hexagonal close-packed crystal structure)
69

31.
L
Leeuwenhoek, Anton Van
Leeuwenhoek, Anton Van (1632-1723), Dutch microscopist and
biologist whose improvements on the light microscope enabled him
and other biologist to make many
important discoveries.
Leeuwenhoek was born in Delft,
Netherlands, on October 24, 1632. His
early schooling was brief and at the
age of 16 he was apprenticed to a
cloth merchant and soon after became
shop booker and cashier.
As a hobby, Leeuwenhoek began
grinding lenses and using them to
study minute objects, particularly
small organisms. The hobby soon became a major activity that
eventually led to many remarkable accomplishments. Leeuwenhoek
used single, small, double convex lenses with very short focus.
The lenses where mounted in flat metal plates equipped with
handles so that the instruments could be held close to the eye.
Firm objects were attached to a pin mounted behind the lens and
fluids were placed on glass in the same position. A screw
adjustment provided for positioning and focusing. By adjusting
the lighting and arranging the background, Leeuwenhoek succeeded
in obtaining magnification and particularly in resolving power
that exceeded those possible with early compound microscope.
In 1668, he extended the Italian anatomist Marcello
Malpighi’s demonstration of capillaries in the circulatory
system. He also observed the circulation of red blood corpuscles

32.
70
in several capillary systems, including those in the tail of an
eel, the web of a frog foot and the ear of a rabbit. In 1674 he
described red blood corpuscles in many other animals.
In 1667, Leeuwenhoek described the spermatozoa of the dog,
rabbit, fish, man, and several other animals. He held the
philosophic position of a preformationist, specifically an
animalculist –that is, he believed that the entire form of an
adult in miniature was present in the sperm and merely unfolded
and grew during the embryonic period.
Among some of the other subjects that Leeuwenhoek studied
with his microscope were muscle fibers, hairs, and epidermal
(skin) cells, the nerves of various animals, ciliated protozoa,
rotifers, plant tissues and the anatomy of insects. Leeuwenhoek
also described the three morphological types of bacteria:
bacillus, cocci, and spirilla; measured the quantity of
perspiration; and demonstrated that blood did not ferment in the
body.
In 1680, Leeuwenhoek became a fellow of the Royal Society
and in 1699 a correspondent of the Academie des Sciences in
Paris. He died in Delft on August 26, 1723.
Lenses
For centuries, human beings have been able to do some pretty
remarkable things with lenses. Although we can’t be sure when or
how the first person stumbled onto the concept, it is clear that
at some point in the past, ancient people (probably from the
Near East) realized that they could manipulate light using a
shaped piece of glass. Over the centuries, how and for what
purpose lenses were used began to increase, as people discovered
that they could accomplish different things using differently
shaped lenses. In addition to making distant objects appear
nearer (i.e. the telescope), they could also be used to make
small objects appear larger and blurry objects appear clear
(i.e. magnifying glasses and corrective lenses). The lenses used
to accomplish these tasks fall into two categories of simple
lenses: Convex and Concave Lenses.

33.
71
A concave lens is a lens that possesses at least one surface
that curves inwards. It is a
diverging lens, meaning that it
spreads out light rays that
have been refracted through it.
A concave lens is thinner at
its centre than at its edges,
and is used to correct short-
sightedness (myopia). The
writings of Pliny the Elder
(23–79) makes mention of what
is arguably the earliest use of
a corrective lens. According to
Pliny, Emperor Nero was said to
watch gladiatorial games using
an emerald, presumably concave
shaped to correct for myopia. After light rays have passed
through the lens, they appear to come from a point called the
principal focus. This is the point onto which the collimated
light that moves parallel to the axis of the lens is focused.
The image formed by a concave lens is virtual, meaning that it
will appear to be farther away than it actually is, and
therefore smaller than the object itself. Curved mirrors often
have this effect, which is why many (especially on cars) come
with a warning: Objects in mirror are closer than they appear.
The image will also be upright, meaning not inverted, as some
curved reflective surfaces and lenses have been known to do. As
every child is sure to find out at some point in their life,
lenses can be an endless source of fun. They can be used for
everything from examining small objects and type to focusing the
sun’s rays. In the latter case, hopefully they choose to be
humanitarian and burn things
like paper and grass rather
than ants! But the fact
remains, a Convex Lens is the
source of this scientific
marvel. Typically made of glass
or transparent plastic, a
convex lens has at least one
surface that curves outward
like the exterior of a sphere.
Of all lenses, it is the most
common given its many uses.

34.
72
A convex lens is also known as a converging lens. A converging
lens is a lens that converges rays of light that are travelling
parallel to its principal axis. They can be identified by their
shape which is relatively thick across the middle and thin at
the upper and lower edges. The edges are curved outward rather
than inward. As light approaches the lens, the rays are
parallel. As each ray reaches the glass surface, it refracts
according to the effective angle of incidence at that point of
the lens. Since the surface is curved, different rays of light
will refract to different degrees; the outermost rays will
refract the most. This runs contrary to what occurs when a
divergent lens (otherwise known as concave, biconcave or Plano-
concave) is employed. In this case, light is refracted away from
the axis and outward.
Lenses are classified by the curvature of the two optical
surfaces. If the lens is biconvex or Plano-convex, the lens is
called positive or converging. Most convex lenses fall into this
category. A lens is biconvex (or double convex, or just convex)
if both surfaces are convex. These types of lenses are used in
the manufacture of magnifying glasses. If both surfaces have the
same radius of curvature, the lens is known as an equiconvex
biconvex. If one of the surfaces is flat, the lens is plano-
convex (or plano-concave depending on the curvature of the other
surface). A lens with one convex and one concave side is convex-
concave or meniscus. These lenses are used in the manufacture of
corrective lenses.
Lewis, Gilbert Newton
Gilbert Newton
Lewis Formers(
October 23, 1875 –
March 23, 1946) was an
American physical chemist known
for the discovery of
the covalent bond and his
concept of electron pairs;
his Lewis dot structures and
other contributions to valence
bond theory have shaped modern
theories of chemical bonding.
Lewis has successfully contributed

35.
73
to thermodynamics, photochemistry, and isotope separation, and
is also known for his concept of acids and bases.
G. N. Lewis was born in 1875 in Weymouth, Massachusetts. After
receiving his PhD in chemistry from Harvard University and
studying abroad in Germany and the Philippines, Lewis moved
to California to teach chemistry at the University of
California, Berkeley. Several years later, he became the Dean of
the college of Chemistry at Berkeley, where he spent the rest of
his life. As a professor, he incorporated thermodynamic
principles into the chemistry curriculum and reformed chemical
thermodynamics in a mathematically rigorous manner accessible to
ordinary chemists. He began measuring the free energy values
related to several chemical processes, both organic and
inorganic.
In 1916, he also proposed his theory of bonding and added
information about electrons in the periodic table of
the elements. In 1933, he started his research on isotope
separation. Lewis worked with hydrogen and managed to purify a
sample of heavy water. He then came up with his theory of acids
and bases, and did work in photochemistry during the last years
of his life. In 1926, Lewis coined the term "photon" for the
smallest unit of radiant energy. He was a brother in Alpha Chi
Sigma, the professional chemistry fraternity.
Though he was nominated 35 times, G. N. Lewis never won
the Nobel Prize in Chemistry. On March 23, 1946, Lewis was found
dead in his Berkeley laboratory where he had been working
with hydrogen cyanide; many postulated that the cause of his
death was suicide. After Lewis' death, his children followed
their father's career in chemistry.
Most of Lewis’ lasting interests originated during his Harvard
years. The most important was thermodynamics, a subject in which
Richards was very active at that time. Although most of the
important thermodynamic relations were known by 1895, they were
seen as isolated equations, and had not yet been rationalized as
a logical system, from which, given one relation, the rest could
be derived. Moreover, these relations were inexact, applying
only to ideal chemical systems. These were two outstanding
problems of theoretical thermodynamics. In two long and
ambitious theoretical papers in 1900 and 1901, Lewis tried to
provide a solution. Lewis introduced the thermodynamic concept
of activity and coined the term "fugacity".[5]
His new idea of
fugacity, or "escaping tendency", was a function with the
dimensions of pressure which expressed the tendency of a
74

36.
substance to pass from one chemical phase to another. Lewis
believed that fugacity was the fundamental principle from which
a system of real thermodynamic relations could be derived. This
hope was not realized, though fugacity did find a lasting place
in the description of real gases.
Lewis’ early papers also reveal an unusually advanced awareness
of J. W. Gibbs’s and P. Duhem’s ideas of free energy
and thermodynamic potential. These ideas were well known to
physicists and mathematicians, but not to most practical
chemists, who regarded them as abstruse and inapplicable to
chemical systems. Most chemists relied on the familiar
thermodynamics of heat (enthalpy) of Berthelot, Ostwald, and
Van’s Hoff, and the calorimetric school. Heat of reaction is
not, of course, a measure of the tendency of chemical changes to
occur, and Lewis realized that only free energy and entropy
could provide an exact chemical thermodynamics. He derived free
energy from fugacity; he tried, without success, to obtain an
exact expression for the entropy function, which in 1901 had not
been defined at low temperatures. Richards too tried and failed,
and not until Nernst succeeded in 1907 was it possible to
calculate entropies unambiguously. Although Lewis’ fugacity-
based system did not last, his early interest in free energy and
entropy proved most fruitful, and much of his career was devoted
to making these useful concepts accessible to practical
chemists.
At Harvard, Lewis also wrote a theoretical paper on the
thermodynamics of blackbody radiation in which he postulated
that light has a pressure. He later revealed that he had been
discouraged from pursuing this idea by his older, more
conservative colleagues, who were unaware that W. Wien and
others were successfully pursuing the same line of thought.
Lewis’ paper remained unpublished; but his interest in radiation
and quantum theory, and (later) in relativity, sprang from this
early, aborted effort. From the start of his career, Lewis
regarded himself as both chemist and
physicist.
Litmus
Litmus, mixture of coloured
organic compounds obtained from
several species of lichens that
75

37.
grow in the Netherlands, particularly Lecanora
tartarea and Roccella tinctorum. Litmus turns red in acidic
solutions and blue in alkaline solutions and is the oldest and
most commonly used indicator of whether a substance is
an acid or a base.
Treatment of the lichens with ammonia, potash, and lime in the
presence of air produces the various coloured components of
litmus. By 1840 litmus had been partially separated into several
substances named azolitmin, erythrolitmin, spaniolitmin, and
erythrolein. These are apparently mixtures of closely related
compounds that were identified.
Logic gate
A logic gate is an idealized or physical device implementing
a Boolean function, that is,
it performs a logical
operation on one or more
logical inputs, and produces a
single logical output.
Depending on the context, the
term may refer to an ideal
logic gate, one that has for
instance zero rise time and
unlimited fan-out, or it may
refer to a non-ideal physical
device[1]
(see Ideal and real
op-amps for comparison).
Logic gates are primarily
implemented
using diodes or transistors acting as electronic switches, but
can also be constructed using electromagnetic relays (relay
logic), fluidic logic, pneumatic logic, optics, molecules, or
even mechanical elements. With amplification, logic gates can be
cascaded in the same way that Boolean functions can be composed,
allowing the construction of a physical model of all of Boolean
logic, and therefore, all of the algorithms and mathematics that
can be described with Boolean logic. Logic circuits include such
devices as multiplexers, registers, arithmetic logic
units (ALUs), and computer memory, all the way up through
complete microprocessors, which may contain more than 100
million gates.
76